Trait core::convert::From

pub trait From<T>: Sized {
    fn from(_: T) -> Self;
}

Used to do value-to-value conversions while consuming the input value. It is the reciprocal of Into.

One should always prefer implementing From over Into because implementing From automatically provides one with a implementation of Into thanks to the blanket implementation in the standard library.

Only implement Into if a conversion to a type outside the current crate is required. From cannot do these type of conversions because of Rust's orphaning rules. See Into for more details.

Prefer using Into over using From when specifying trait bounds on a generic function. This way, types that directly implement Into can be used as arguments as well.

The From is also very useful when performing error handling. When constructing a function that is capable of failing, the return type will generally be of the form Result<T, E>. The From trait simplifies error handling by allowing a function to return a single error type that encapsulate multiple error types. See the "Examples" section and the book for more details.

Note: This trait must not fail. If the conversion can fail, use TryFrom.

Generic Implementations

• From<T> for U implies Into<U> for T
• From is reflexive, which means that From<T> for T is implemented

Examples

String implements From<&str>:

An explicit conversion from a &str to a String is done as follows:

let string = "hello".to_string();
let other_string = String::from("hello");

assert_eq!(string, other_string);

While performing error handling it is often useful to implement From for your own error type. By converting underlying error types to our own custom error type that encapsulates the underlying error type, we can return a single error type without losing information on the underlying cause. The '?' operator automatically converts the underlying error type to our custom error type by calling Into<CliError>::into which is automatically provided when implementing From. The compiler then infers which implementation of Into should be used.

use std::fs;
use std::io;
use std::num;

enum CliError {
    IoError(io::Error),
    ParseError(num::ParseIntError),
}

impl From<io::Error> for CliError {
    fn from(error: io::Error) -> Self {
        CliError::IoError(error)
    }
}

impl From<num::ParseIntError> for CliError {
    fn from(error: num::ParseIntError) -> Self {
        CliError::ParseError(error)
    }
}

fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
    let mut contents = fs::read_to_string(&file_name)?;
    let num: i32 = contents.trim().parse()?;
    Ok(num)
}

Required methods

fn from(_: T) -> Self

Performs the conversion.

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Implementors

impl From<!> for Infallible

fn from(x: !) -> Self

impl From<!> for TryFromIntError

fn from(never: !) -> TryFromIntError

impl From<Infallible> for TryFromSliceError

fn from(x: Infallible) -> TryFromSliceError

impl From<Infallible> for TryFromIntError

fn from(x: Infallible) -> TryFromIntError

impl From<NonZeroI128> for i128

fn from(nonzero: NonZeroI128) -> Self

impl From<NonZeroI16> for i16

fn from(nonzero: NonZeroI16) -> Self

impl From<NonZeroI32> for i32

fn from(nonzero: NonZeroI32) -> Self

impl From<NonZeroI64> for i64

fn from(nonzero: NonZeroI64) -> Self

impl From<NonZeroI8> for i8

fn from(nonzero: NonZeroI8) -> Self

impl From<NonZeroIsize> for isize

fn from(nonzero: NonZeroIsize) -> Self

impl From<NonZeroU128> for u128

fn from(nonzero: NonZeroU128) -> Self

impl From<NonZeroU16> for u16

fn from(nonzero: NonZeroU16) -> Self

impl From<NonZeroU32> for u32

fn from(nonzero: NonZeroU32) -> Self

impl From<NonZeroU64> for u64

fn from(nonzero: NonZeroU64) -> Self

impl From<NonZeroU8> for u8

fn from(nonzero: NonZeroU8) -> Self

impl From<NonZeroUsize> for usize

fn from(nonzero: NonZeroUsize) -> Self

impl From<bool> for AtomicBool

fn from(b: bool) -> Self

Converts a bool into an AtomicBool.

Examples

use std::sync::atomic::AtomicBool;
let atomic_bool = AtomicBool::from(true);
assert_eq!(format!("{:?}", atomic_bool), "true")

impl From<bool> for i8

Converts a bool to a i8. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i8::from(true), 1);
assert_eq!(i8::from(false), 0);

fn from(small: bool) -> i8

impl From<bool> for i16

Converts a bool to a i16. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i16::from(true), 1);
assert_eq!(i16::from(false), 0);

fn from(small: bool) -> i16

impl From<bool> for i32

Converts a bool to a i32. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i32::from(true), 1);
assert_eq!(i32::from(false), 0);

fn from(small: bool) -> i32

impl From<bool> for i64

Converts a bool to a i64. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i64::from(true), 1);
assert_eq!(i64::from(false), 0);

fn from(small: bool) -> i64

impl From<bool> for i128

Converts a bool to a i128. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(i128::from(true), 1);
assert_eq!(i128::from(false), 0);

fn from(small: bool) -> i128

impl From<bool> for isize

Converts a bool to a isize. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(isize::from(true), 1);
assert_eq!(isize::from(false), 0);

fn from(small: bool) -> isize

impl From<bool> for u8

Converts a bool to a u8. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u8::from(true), 1);
assert_eq!(u8::from(false), 0);

fn from(small: bool) -> u8

impl From<bool> for u16

Converts a bool to a u16. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u16::from(true), 1);
assert_eq!(u16::from(false), 0);

fn from(small: bool) -> u16

impl From<bool> for u32

Converts a bool to a u32. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u32::from(true), 1);
assert_eq!(u32::from(false), 0);

fn from(small: bool) -> u32

impl From<bool> for u64

Converts a bool to a u64. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u64::from(true), 1);
assert_eq!(u64::from(false), 0);

fn from(small: bool) -> u64

impl From<bool> for u128

Converts a bool to a u128. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(u128::from(true), 1);
assert_eq!(u128::from(false), 0);

fn from(small: bool) -> u128

impl From<bool> for usize

Converts a bool to a usize. The resulting value is 0 for false and 1 for true values.

Examples

assert_eq!(usize::from(true), 1);
assert_eq!(usize::from(false), 0);

fn from(small: bool) -> usize

impl From<char> for u32

fn from(c: char) -> Self

Converts a char into a u32.

Examples

use std::mem;

fn main() {
    let c = 'c';
    let u = u32::from(c);
    assert!(4 == mem::size_of_val(&u))
}

impl From<f32> for f64

Converts f32 to f64 losslessly.

fn from(small: f32) -> f64

impl From<i8> for isize

Converts i8 to isize losslessly.

fn from(small: i8) -> isize

impl From<i16> for isize

Converts i16 to isize losslessly.

fn from(small: i16) -> isize

impl From<i16> for AtomicI16

fn from(v: i16) -> Self

Converts an i16 into an AtomicI16.

impl From<i16> for f32

Converts i16 to f32 losslessly.

fn from(small: i16) -> f32

impl From<i16> for f64

Converts i16 to f64 losslessly.

fn from(small: i16) -> f64

impl From<i16> for i32

Converts i16 to i32 losslessly.

fn from(small: i16) -> i32

impl From<i16> for i64

Converts i16 to i64 losslessly.

fn from(small: i16) -> i64

impl From<i16> for i128

Converts i16 to i128 losslessly.

fn from(small: i16) -> i128

impl From<i32> for AtomicI32

fn from(v: i32) -> Self

Converts an i32 into an AtomicI32.

impl From<i32> for f64

Converts i32 to f64 losslessly.

fn from(small: i32) -> f64

impl From<i32> for i64

Converts i32 to i64 losslessly.

fn from(small: i32) -> i64

impl From<i32> for i128

Converts i32 to i128 losslessly.

fn from(small: i32) -> i128

impl From<i64> for AtomicI64

fn from(v: i64) -> Self

Converts an i64 into an AtomicI64.

impl From<i64> for i128

Converts i64 to i128 losslessly.

fn from(small: i64) -> i128

impl From<i8> for AtomicI8

fn from(v: i8) -> Self

Converts an i8 into an AtomicI8.

impl From<i8> for f32

Converts i8 to f32 losslessly.

fn from(small: i8) -> f32

impl From<i8> for f64

Converts i8 to f64 losslessly.

fn from(small: i8) -> f64

impl From<i8> for i16

Converts i8 to i16 losslessly.

fn from(small: i8) -> i16

impl From<i8> for i32

Converts i8 to i32 losslessly.

fn from(small: i8) -> i32

impl From<i8> for i64

Converts i8 to i64 losslessly.

fn from(small: i8) -> i64

impl From<i8> for i128

Converts i8 to i128 losslessly.

fn from(small: i8) -> i128

impl From<isize> for AtomicIsize

fn from(v: isize) -> Self

Converts an isize into an AtomicIsize.

impl From<u8> for usize

Converts u8 to usize losslessly.

fn from(small: u8) -> usize

impl From<u8> for isize

Converts u8 to isize losslessly.

fn from(small: u8) -> isize

impl From<u8> for char

Maps a byte in 0x00...0xFF to a char whose code point has the same value, in U+0000 to U+00FF.

Unicode is designed such that this effectively decodes bytes with the character encoding that IANA calls ISO-8859-1. This encoding is compatible with ASCII.

Note that this is different from ISO/IEC 8859-1 a.k.a. ISO 8859-1 (with one less hyphen), which leaves some "blanks", byte values that are not assigned to any character. ISO-8859-1 (the IANA one) assigns them to the C0 and C1 control codes.

Note that this is also different from Windows-1252 a.k.a. code page 1252, which is a superset ISO/IEC 8859-1 that assigns some (not all!) blanks to punctuation and various Latin characters.

To confuse things further, on the Web ascii, iso-8859-1, and windows-1252 are all aliases for a superset of Windows-1252 that fills the remaining blanks with corresponding C0 and C1 control codes.

fn from(i: u8) -> Self

Converts a u8 into a char.

Examples

use std::mem;

fn main() {
    let u = 32 as u8;
    let c = char::from(u);
    assert!(4 == mem::size_of_val(&c))
}

impl From<u16> for usize

Converts u16 to usize losslessly.

fn from(small: u16) -> usize

impl From<u16> for AtomicU16

fn from(v: u16) -> Self

Converts an u16 into an AtomicU16.

impl From<u16> for f32

Converts u16 to f32 losslessly.

fn from(small: u16) -> f32

impl From<u16> for f64

Converts u16 to f64 losslessly.

fn from(small: u16) -> f64

impl From<u16> for i32

Converts u16 to i32 losslessly.

fn from(small: u16) -> i32

impl From<u16> for i64

Converts u16 to i64 losslessly.

fn from(small: u16) -> i64

impl From<u16> for i128

Converts u16 to i128 losslessly.

fn from(small: u16) -> i128

impl From<u16> for u32

Converts u16 to u32 losslessly.

fn from(small: u16) -> u32

impl From<u16> for u64

Converts u16 to u64 losslessly.

fn from(small: u16) -> u64

impl From<u16> for u128

Converts u16 to u128 losslessly.

fn from(small: u16) -> u128

impl From<u32> for AtomicU32

fn from(v: u32) -> Self

Converts an u32 into an AtomicU32.

impl From<u32> for f64

Converts u32 to f64 losslessly.

fn from(small: u32) -> f64

impl From<u32> for i64

Converts u32 to i64 losslessly.

fn from(small: u32) -> i64

impl From<u32> for i128

Converts u32 to i128 losslessly.

fn from(small: u32) -> i128

impl From<u32> for u64

Converts u32 to u64 losslessly.

fn from(small: u32) -> u64

impl From<u32> for u128

Converts u32 to u128 losslessly.

fn from(small: u32) -> u128

impl From<u64> for AtomicU64

fn from(v: u64) -> Self

Converts an u64 into an AtomicU64.

impl From<u64> for i128

Converts u64 to i128 losslessly.

fn from(small: u64) -> i128

impl From<u64> for u128

Converts u64 to u128 losslessly.

fn from(small: u64) -> u128

impl From<u8> for AtomicU8

fn from(v: u8) -> Self

Converts an u8 into an AtomicU8.

impl From<u8> for f32

Converts u8 to f32 losslessly.

fn from(small: u8) -> f32

impl From<u8> for f64

Converts u8 to f64 losslessly.

fn from(small: u8) -> f64

impl From<u8> for i16

Converts u8 to i16 losslessly.

fn from(small: u8) -> i16

impl From<u8> for i32

Converts u8 to i32 losslessly.

fn from(small: u8) -> i32

impl From<u8> for i64

Converts u8 to i64 losslessly.

fn from(small: u8) -> i64

impl From<u8> for i128

Converts u8 to i128 losslessly.

fn from(small: u8) -> i128

impl From<u8> for u16

Converts u8 to u16 losslessly.

fn from(small: u8) -> u16

impl From<u8> for u32

Converts u8 to u32 losslessly.

fn from(small: u8) -> u32

impl From<u8> for u64

Converts u8 to u64 losslessly.

fn from(small: u8) -> u64

impl From<u8> for u128

Converts u8 to u128 losslessly.

fn from(small: u8) -> u128

impl From<usize> for AtomicUsize

fn from(v: usize) -> Self

Converts an usize into an AtomicUsize.

impl<'a, T> From<&'a Option<T>> for Option<&'a T>

fn from(o: &'a Option<T>) -> Option<&'a T>

impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>

fn from(o: &'a mut Option<T>) -> Option<&'a mut T>

impl<T> From<*mut T> for AtomicPtr<T>

fn from(p: *mut T) -> Self

impl<T> From<T> for Option<T>

fn from(val: T) -> Option<T>

impl<T> From<T> for Poll<T>

fn from(t: T) -> Poll<T>

impl<T> From<T> for Cell<T>

fn from(t: T) -> Cell<T>

impl<T> From<T> for RefCell<T>

fn from(t: T) -> RefCell<T>

impl<T> From<T> for UnsafeCell<T>

fn from(t: T) -> UnsafeCell<T>

impl<T> From<T> for T

fn from(t: T) -> T

impl<T: ?Sized, '_> From<&'_ T> for NonNull<T>

fn from(reference: &T) -> Self

impl<T: ?Sized, '_> From<&'_ mut T> for NonNull<T>

fn from(reference: &mut T) -> Self

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